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FIGURE 1: The SMARTFIRE mesh and the MD11 aircraft.
The pre-fire airflow CFD analysis was performed first. The initial and boundary airflow conditions at the various flow components in the CFD model were provided by the TSB (e.g., conditioned air supply rates into and out of the cockpit). The model was then run and the velocity vectors and flow rates were studied at different locations within the virtual aircraft. Some adjustments were made to those boundary flow rates until the airflow patterns in the computer model closely matched those observed in actual aircraft during airflow flight tests.
The fire initiation site, as provided by TSB, was prescribed with the aid of a volumetric heat source. The source was adjusted so as to sustain the combustion of the materials over a short duration to allow flame propagation. Criteria for the fire propagation are: 1) critical radiative heat flux from the surrounding fire that would ignite nearby material; 2) critical surface ignition temperature; 3) a combustible surface cell is allowed to ignite if it is in the vicinity of a region of a flame tip for two seconds or more; 4) the surface cell is also allowed to ignite based on experimental flame spread data for similar thin-films considered here.
Six fire simulations were carried out in transient mode. The initial flow conditions for these fire simulations were obtained from the pre-fire simulations performed as part of the fire simulation. These cases consisted of various modifications leading to the final scenario of interest. Only the final simulation results with all the required revisions implemented are reported here.
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Figure 1: Flow rate at cockpit ceiling crack. | Figure 2: Flow rates at the smoke barrier. |
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(a) at 850 seconds | (b) at 1500 seconds |
Figure 3: Fire spread at (a) 850s and (b) 1500s
Shown in Figure 1 are low smoke concentration surface maps during the early stages of the fire. It depicts the onset of small traces of smoke entering the cockpit at (i) the crack adjacent to the Avionics CB Panel, close to the right overhead diffuser, and (ii) through the small opening in the cockpit ceiling liner located above and to the left of the Captain’s seat. Figure 2 depicts the flow rates vs. time at the smoke barrier. In this simulation, at approximately 5 minutes after the fire started, part of the smoke barrier collapsed due to high temperatures. The positive value indicates that air was being drawn aft, out of the cockpit through the newly created opening. Figure 3 shows the fire damage on the insulation blankets and the riser ducts at 850 seconds just after the Cabin Bus was switched OFF. The predicted damage both aft and forward of the cockpit wall was 3.8 and 1.4 metres respectively at 850 seconds and 5.6 and 1.6 metres at 1500 seconds respectively. This compares well with data available from the SR 111 investigation, where extensive fire damage in the area above the ceiling in the front section of the aircraft was concentrated about 1.5 metres forward and 5 metres aft of the cockpit wall.
SMARTFIRE animation of fire development.
Real
Media (low quality) - streamed from the server [34 sec]
Real
Media (good quality) - downloadable [1.87 MB]
With the successful completion of this project, SMARTFIRE has become the first fire model to be used in an air crash investigation. The official TSB report acknowledged the technology’s successful debut in ‘helping to develop better insight into and understanding of the fire’. This study has demonstrated that CFD based fire analysis is a cost effective approach to investigating complex flow/fire scenarios and that coupled with well targeted controlled experiments generating quality experimental data, CFD fire simulation can be a powerful tool in aircraft accident investigation. This study represents a significant milestone in the use of Computational Fire Engineering (CFE) tools, such as SMARTFIRE in forensic analysis.
Reference:
"Flight Simulation". Jia F., Patel, M. and Galea E.R. Fire Prevention Fire Engineers Journal, October 2003, pp27-29, 2003.
See publications #162, 95, 83, 71, 64-62, 30, 29, 27, 25, 22, 19, 17, 16, 10.
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